Work-related asthma is asthma that is attributable to, or is made worse by, environmental exposures in the workplace. Published estimates of the proportion of adult asthma attributable to occupational factors have varied widely, depending on population, methodology, and definitions, from 2 percent to 33 percent. Occupational asthma is of great public health importance because it is potentially preventable, can cause substantial disability, and in some cases is completely curable. Among adults in the United States, asthma has become a major public health problem, with rates most elevated among low income, urban, African American and Latino sectors of the population, and with substantial evidence suggesting potential occupational contributions to the excess rates. These important sectors of the U.S. population have, however, been inadequately represented in the occupational asthma research literature.